12.17.03; All Photos Courtesy Ben Taube, City of Atlanta, Unless
Cool Roof in a Hot City: The Southeast's First Municipal Greenroof
By Benjamin Taube and Janet Ward
It’s hotter in the city.
Expanses of concrete and asphalt-shingled roofs, combined with a lack of
open greenspace, produce a phenomenon that has been documented by
everyone from local meteorologists to scientists at NASA. Called the
“Heat Island Effect,” it raises urban temperatures to much higher daily
levels than those enjoyed in less developed areas.
The phenomenon, along with urban ills like degraded air and water
quality, can be mitigated by building gardens and protecting greenspace.
The problem is that in highly developed urban areas, there is nowhere to
put those gardens and no greenspace to protect.
City Hall Greenroof Conceptual Master Plan
Atlanta officials found a solution in City Hall. Using the fourth-floor
roof of the newest part of the building, they constructed a “greenroof,”
planting more than 2,000 square feet of vegetation, mostly hardy sedums
and herbs, and creating a garden in the air.
Although the idea has
been incorporated into municipal architecture in cities like Chicago,
Portland, OR, and Seattle, Atlanta’s greenroof is the first such project
in the Southeast.
Faust Laying the J-Drain Drainage Layer; Right: Afterwards;
Photos Courtesy JDR Enterprises, Inc.
Debuting in December 2003 after more than two years of research and
planning, the city’s greenroof will serve as a pilot project that its
creators hope will generate reliable technical data in areas such as
temperature reduction, energy efficiency, and stormwater retention. They
also will monitor its effect on roof life and hope to determine which
plants work best in the shallow soil of a greenroof. Finally, and most
importantly, they hope to show Atlanta’s business community a working
greenroof that can serve as a model for similar projects.
Atlanta City Hall Pre-Planting After It'Saul Natural Growth
Media Installation, 12.15.03;
Right: After, Courtesy Janet Faust
The Atlanta project was driven by Ben Taube, the city’s Environmental
Manager, and Bill Brigham, its Landscape Architect. It contains 35
varieties of vegetation, mostly hardy sedums and herbs, and was designed
as an “extensive greenroof,” which features low soil depths and
low-growing vegetation. The project was completed with the assistance of
more than 10 companies and vendors who donated plants and other products
and services. The City sited the greenroof outside the building’s
fifth-floor cafeteria and not atop the main roof so it could serve as a
Vegetation Close Up 12.18.03
The greenroof idea is important because Atlanta produces enormous
amounts of ground-level ozone every summer and has been designated a
“severe” non-attainment area by the Environmental Protection Agency. In
2002, the city exceeded federal ozone standards on 38 days, up from 20
days in 2001.
In 2001, Atlanta joined with the Georgia Environmental Protection
Division and other partners in a NASA-funded project to develop and
validate an improved urban air quality modeling system using
high-resolution remote sensing data. The project concludes this year
with what the city hopes will be a system that allows stakeholders to
quantify the impact of land cover and land use changes on air quality,
particularly ground-level ozone.
Taube and Brigham also expect the greenroof to play a significant role
in mitigating stormwater problems by absorbing water that normally would
wash into the sewer system. Additionally, they hope that eventually the
city will create an incentive program – like those in other cities – for
commercial, residential and industrial greenroof projects. Such
incentives will become increasingly popular, since the city is working
on creating a stormwater utility that will base future fees on
impervious surface calculations. Traditional roofs represent large
impervious surfaces, so greenroofs can be significant factor in
off-setting future fees.
Jack Ravan, commissioner of the Department of Watershed Management,
which sponsored the project, is a serious fan of the greenroof idea, as
is Atlanta Mayor Shirley Franklin, who has indicated an interest in
growing tomatoes on the roof. “Greenroof technology is a viable tool for
mitigating the urban heat island effect and for dealing with stormwater
problems,” says Ravan, who also is a former EPA Regional Administrator.
Atlanta’s summers can be brutally hot, and it is not uncommon for
temperatures within the city core to be higher than those in the
surrounding suburbs. The greenroof serves as a heat-absorbing buffer and
an environmentally friendly replacement for asphalt or concrete roofing.
“The [temperature] reductions will come in the summer when we have the
intense sun,” Brigham says.
The project represented a relatively minor expenditure, primarily
because, with outside bidding starting at $163,000, the city focused on
in-house program management, construction and maintenance. The City
received approximately $55,000 in donated products, a construction grant
of $18,000 from the State, and a matching grant of $18,000 from the
Department of Watershed Management. The project cost a total of
$110,000, but minus the donations and grants it cost the City $19,000.
The city’s Parks and Recreation department will provide what little
maintenance the roof is expected to require. Click
view the Cost Breakdown pdf.
The greenroof was constructed in four phases over a six-week period.
After a structural analysis concluded that the roof could support
“extensive” soil (the lighter of the two types of soil used in greenroof
applications), workers removed concrete ramps and asphalt, replacing it
with waterproofing material donated by Teaneck, N.J.-based KEMCO Kemper
Systems. The construction team then plugged existing drains and flooded
the roof’s surface to ensure that there were no leaks.
North-Facing Side View of Atlanta City Hall Greenroof,
Other material and services were donated by local firms Excel Electrical
Saul Nurseries (plants), It'Saul Natural
(lightweight engineered soil),
Enterprises (drainage system), Unique
Environmental (plant installation), Flintstone Pavers (paver
installation), Sims Stones (pavers) and by the City’s Department of
General Services (labor).
On February 19, 2004, the City of Atlanta hosted a roundtable discussion
on the City Hall greenroof project. The Atlanta Chapter of the U.S.
Green Building Council (USGBC) sponsored the event, and the audience
consisted of product manufactures, developers, architects, engineers,
municipal government staff, City Council representatives, and
contractors. The speaker panel consisted of Ben Taube; Janet Faust of
Enterprises; Ernie Higgins of It'Saul Natural; and Chris Kramer from
Kemper waterproofing systems.
Participants had an
opportunity to speak for 10 minutes on their product and use on the City
Hall greenroof. Ben Taube started off the roundtable with a discussion
of the City’s sustainability initiatives, which includes the development
of another greenroof. Additionally, Ben discussed the greenroof project
and construction steps. Next Janet Faust discussed the drainage layer
that was used on the City Hall greenroof project; the J-Drain system was
supplied by JDR Enterprise and was applied on the entire surface of the
roof deck. More information on the J-Drain system can be obtained from
discussion, Chris Kramer from Moon and Associates representing Kemper
Waterproofing systems discussed the waterproofing layer used on the
project. The waterproofing system is a liquid applied membrane
consisting of three layers, and is certified for contact with potable
water. More information is available at
The last presentation was a
discussion on the structural soil mixture that was used on the project.
The growth media was supplied by Ernie Higgins from It'Saul Natural
located in Dahlonega, Georgia. Information on the soil can be
obtained from Ernie at
Concluding the speakers’
presentations the audience participated in a question and answer
session. The majority of questions centered on the construction stages
of a greenroof as well as product specific information regarding the
soil and drainage layer. Each participant showed an extreme interest in
the greenroof project and took away a good basic education on the means
of designing and constructing a greenroof.
From February 18th
through 22nd, 2004, the City of Atlanta Department of
Watershed Management participated at the Southeastern Flower Show with a
“Discovery Garden” exhibiting the City Hall greenroof. Throughout
the 4-day show, the exhibit was visited by a variety of landscape
professionals and residential homeowners. Visitors to the “Discovery
Garden” were very excited to see that the City was taking steps to
mitigate the urban heat island. Many visitors wanted to learn about the
variety of sedum plants that were used on the project.
Southeastern Flower Show Table Top Greenroof Exhibit
“It’s going to be a pleasant
place to be this spring and summer,” Taube says. “We’re hoping other
people see it and say, ‘Hey, I want one of those,’ but we also want them
to realize the many environmental benefits offered by greenroof
City Hall Pilot Greenroof Overview, 12.17.03
Benjamin Taube is the
City of Atlanta’s Environmental Manager and can be reached at 55 Trinity
Ave. SW, Suite 5900, Atlanta, Georgia 30303; Phone 404.330.6752; Fax
His responsibilities include developing and enhancing environmental
initiatives and policy in Atlanta.
Janet Ward is the
Department of Watershed Management's Public Information Manager and can
be reached at 55 Trinity Ave. SW, Suite 5400, Atlanta, Georgia 30303;
Phone 404.330.6620; Fax 404.658.6515; or
Her responsibilities include public relationship and outreach for the